Master cylinder piston and device for mounting a check valve therein

ABSTRACT

A master cylinder piston for use in a motor vehicle having a flap ( 22 ) that is biased towards a position to shut off a pressure-fluid passage ( 24 ) by a return spring ( 28 ) resting on a cage ( 30 ). A flange ( 38 ) on a cage ( 30 )for the Spring ( 28 ) is located in an annular groove ( 44 ) provided in the housing ( 20 ) for the flap ( 22 ) when the cage ( 30 ) bears axially on an inner shoulder ( 64 ) of the housing ( 20 ).

This invention relates to a master cylinder piston of a braking circuit,more particularly for a motor vehicle, as well as to a jig for thefitting of a flap into said piston.

BACKGROUND OF THE INVENTION

In a master cylinder, more particularly of the tandem type, each of theprimary and secondary pistons is fitted with a moving shutter, or flap,for the opening and closing of a pressure-fluid passage provided in thepiston, as a function of the strokes of the piston inside the mastercylinder.

Such fluid passage opens axially into a housing formed at one end of thepiston and accommodating the flap, which comprises a rod, guided withinthe fluid passage, and a head situated outside the passage and biased bya return spring towards the fluid passage outlet so as to close it in atight manner.

Such return spring is a compression spring arranged between the flaphead and bearing means, added to the piston.

It has already been suggested that these bearing means be constituted bya metal cage resiliently snapped in the flap housing. For this purpose,the cage comprises resiliently-deformable lugs, situated at itsperiphery, facing radially outwards and intended to enter and getlatched in an annular groove provided in the cylindrical wall of theflap housing. In the course of the assembling process, such lugs areresiliently brought closer to the axis, as the cage is inserted in theflap housing and they rub against the cylindrical wall of the housingtill the cage assumes an axial position inside the housing, in which thelugs engage the above-mentioned annular groove in a snapping manner.

The rubbing motions of the steel cage lugs against the cylindrical wallof the housing provided in the piston, made of aluminium or of a lightalloy, are likely to scratch the cylindrical wall and tear away metalparticles or chips, which may settle under the flap head or on the upperlip of a seal cup, or be the cause of scratches during the piston traveland consequently give rise to tightness failures in the master cylinder,actually a major drawback which it is essential to cure.

Besides, such cage should neither interfere with the brake-fluid flownor restrict its flow rate.

SUMMARY OF THE INVENTION

Therefore, it is the main object of the present invention to provide asimple, efficient and inexpensive solution to the above-mentionedproblem, in that any potential scratch or tightness failure of themaster cylinder is prevented, which would result from the mounting ofsaid cage on the piston of the master cylinder.

With this object in view, the present invention provides a mastercylinder piston, more particularly for a motor vehicle, comprising atone end a substantially cylindrical housing accommodating a flap and areturn spring arranged between the flap and a cage, added to the piston,characterised in that said cage is crimped inside said housing.

Crimping actually means a plastic deformation of part of the cage, whichmay be performed when the cage is in the desired axial position insidethe housing, which precludes any risk of tearing away metal particles orchips, likely to give rise to scratches and tightness failures in themaster cylinder.

In accordance with another feature of the invention, the crimpingprocess is carried out using retaining, means, which are formed on thecage and accommodated, under a plastic deformation effect, in an annulargroove provided in said housing.

According to a first embodiment of the present invention, the retainingmeans of the cage comprise a substantially cylindrical flange extendinground the cage in the direction of the open end of the housing.

In another embodiment of this invention, such retaining means compriselugs, extending substantially parallel to the axis of the cage aroundthe latter in the direction of the open end of the housing.

Advantageously, such lugs are formed either by partial cuts or cutoutsmade in a substantially cylindrical or truncated-cone shaped wall of thecage.

Preferably, the retaining means are formed at one end of the cage andjoined up with it by an annular flange extending radially inwards andcomprising means for an applying to supporting means, formed inside theflap housing.

It results in that the cage may be set automatically in its crimpingposition inside the housing.

At its end facing away from said retaining means, the cage comprisesanother annular flange directed radially inwards and constitutingbearing means for the return spring of the flap.

In an advantageous manner, the cage according to the invention ismanufactured using a stamping process, in a simple and inexpensive way.

The invention also provides a jig for the fitting of a flap into amaster cylinder piston, more particularly for a motor vehicle, suchpiston comprising, at one end, a substantially cylindrical housingaccommodating a flap and a return spring arranged between the flap and acages added to the piston and fastened using retaining means receivedwithin an annular groove made in the cylindrical wall of the housing,said device being characterised in that:

-   -   in an initial free state, the cage has an outer diameter which        is smaller than the inner diameter of the housing;    -   the housing includes means for the axial support of the cage in        a position in which its retaining means are radially in line        with said annular groove;    -   the jig comprises means for the support and application of the        cage onto the supporting means of the housing, and means for a        radially-outward deformation of said retaining means, so as to        introduce them into the annular groove provided in the housing.

In an advantageous manner, the means for the support and application ofthe cage onto the supporting means of the housing comprise a centralpush rod, fitted inside a tubular member, a bevelled end of whichconstitutes said radial-deformation means.

Preferably, the central push rod is guided for an axial sliding motionwithin said tubular member, and biased by a return spring in a directionwhich corresponds to the applying of the cage onto the supporting means,formed in the housing.

According to this invention, one only has to proceed to the axialalignment of the jig with the master cylinder piston, and then move, inan axial translation motion, the jig towards the piston or vice versa,so as to insert the cage in the flap housing, position it axially insidesaid housing through its retaining means radially in line with theannular groove, provided in the housing for their accommodation, andmove the jig farther on towards the piston for a plastic deformation ofthe retaining means of the cage and their radial introduction into theannular groove provided in the housing.

Afterwards, a reverse axial translation motion causes the piston toseparate from the jig, whereas the cage is retained within the flaphousing.

Other features, advantages and details of the present invention will beapparent from the following detailed description, by way of example andby no means as a limitation, when taken in conjunction with theaccompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic axial sectional view, showing a master cylinderpiston according to this invention;

FIG. 2 is a schematic view on a larger scale of the detail within circleII of FIG. 1;

FIG. 3 is a schematic axial sectional view of a jig according to thisinvention;

FIG. 4 is a schematic partial axial sectional view, on a larger scale,showing the fitting of the cage into the flap housing of a pistonaccording to this invention;

FIG. 5 is a schematic perspective view of a variant of the cage;

FIG. 6 is a schematic axial sectional view, showing another variant ofthe cage; and

FIGS. 7 and 8 are schematic perspective views of another variant of thecage.

DETAILED DESCRIPTION OF THE INVENTION

As a rule, in the drawings, the forward direction is indicated by arrowAV while arrow AR shows the rear direction.

FIG. 1 is a schematic illustration of an embodiment of a secondarypiston 10 of a tandem master cylinder of a braking circuit for a motorvehicle, the piston 10 comprising a body 12, which is connected by meansof an adjusting screw 14 to a spring stop 16, biased by a spring 18,arranged between the stop 16 and an end of the secondary piston body 12,such spring stop 16 being intended for a cooperation with a primarypiston (not shown) of the master cylinder.

At the end facing away from the spring stop 16, the secondary pistonexhibits a tubular axial end 20, which defines a substantiallycylindrical housing for the accommodation of a flap 22, opening andclosing an axial passage 24, made in a transverse wall of the body 12.The flap 22 includes an axial rod 26, inserted in the passage 24, and itis connected to a return spring 28, arranged between the head of theflap 22 and a cage 30, inserted inside the housing 20.

In the position illustrated in FIG. 1, the head of the flap 22 isresiliently pushed by the return spring 28 to bear on the outlet of thepassage 24 in the housing 20, for a tight shut-off of said passage.

The cage 30 is a metal part, for instance a stamped steel one, and itcomprises a truncated-cone shaped wall 32 widening rearwards, and thefront end of which is connected to an annular flange 34 extendingradially inwards, whereas the rear end of the truncated-cone shaped wall32 is joined up with an annular flange 36 extending radially outwards,itself linked up with a cylindrical flange 38 which extends in theforward direction about the truncated-cone shaped wall 32 and spacedapart from it.

In the crimping position of the cage 30, as shown in FIGS. 1 and 2, thefront end 40 of the cylindrical flange 38 is deformed radially outwardsand it extends slantwise so as to abut against the front edge 42 of anannular groove 44, provided in the inner surface of the wall of thehousing 20, such groove having a rear edge 46 extending slantwiserearwards. The inner diameter of the cylindrical wall of the housing 20is slightly greater than the outer diameter of the cylindrical flange 38in the unstrained free condition. In said position, the cage 30 may bemoved axially inside the housing 20 on a distance which corresponds tothe axial play of the end 40 of the flange 38 within the groove 44, withthe result that openings 48, made at regular intervals in the annularflange 36, may be kept clear of the end part of the housing 20, so as tofacilitate the pressure-fluid flow through the passage 24 when the flap22 is open, such pressure fluid also flowing through the centralopening, defined by the annular flange 34 of the cage 30.

FIG. 3 shows an embodiment of a jig for the fitting of the cage 30, in aschematic manner.

Such jig 50 comprises a central push rod 52, slidably fitted inside atubular member 54, the rear end 56 of which is bevelled outwards andconstitutes the means for the plastic deformation of the end 40 of thecylindrical flange 38 of the cage 30.

A compression spring 58 is arranged inside the tubular member 54,between the push rod 52 and a front stop 60, the axial position of whichcan be adjusted when it is screwed in the tubular member 54, and so thepush rod 52 is permanently biased rearwards by the spring 58 in order torest against an inner shoulder 62 of the tubular member 54. The rear endof the push rod 52 comprises support means for the cage 30.

The mode of operation of said jig is represented in FIG. 4, the lowerpart of which shows the cage 30 before it is crimped, while the upperpart shows the cage 30 as it is being crimped.

Initially, the flap 22 is introduced by its rod 26 into the passage 24and the spring 28 is fitted on the head of the flap 22.

The jig according to FIG. 3 is axially aligned with the secondary piston10 in such a way that the cage 30, carried by the end part of the pushrod 52, faces the open end of the housing 20 at the front end of thepiston 10. Then the device is subjected to an axial translation motiontill it reaches the position shown in the lower part of FIG. 4, in whichthe spring 28 is compressed between the head of the flap 22 and theannular flange 34 of the cage 30, the latter resting at its annularflange 36 on an inner shoulder 64 of the housing 20. For the time being,the front end of the cylindrical flange 38 of the cage 30 liessubstantially at the level of the middle part of the annular groove 44provided in the housing 20.

Thereafter, the tubular member 54 of the jig is moved farther onrearwards so that its bevelled end 56 may enter the cylindrical flange38, with the result that it deforms the end 40 of such flange radiallyoutwards within the annular groove 44, and that it axially abuts againstthe annular flange 36 of the cage 30, the latter flange abutting againstthe inner shoulder 64 of the housing 20, as shown in the upper part ofFIG. 4.

In such a position, the outward deformation of the end 40 of thecylindrical flange 38 of the cage is a permanent set. In a preferredmanner, such a process is carried out without the end 40 of the flange38 bearing on the root of the groove 44.

Next, the jig 50 is axially moved in the forward direction so as to beextracted from the housing 20. Under the force exerted by the spring 28,the cage 30 follows that translation motion till the end 40 of itscylindrical flange 38 comes to rest on the front edge of the annulargroove 44, in the position illustrated in FIG. 2. This being so, theflap 22 is kept in a position in which the passage 24 is shut off in aleakproof manner, but a translation motion in the forward direction maybe imparted to the flap, while the spring 28 is compressed, when thepassage has to be opened.

The radial outward deformation of the end 46 of the flange 38 of thecage 30 implies no rubbing motion of part of said cage on the piston 10,when the jig 50 is guided accurately in relation to the piston 10, whichis very simple to achieve. Moreover, an automated control of the jig isquite feasible.

As regards the variant illustrated in FIG. 5, the cage 30 comprises acylindrical or truncated-cone shaped wall 32, the rear end of whichexhibits U-shaped lugs 66, a first part 68 of which extends axiallyrearwards in the prolongation of the wall 32, whereas an intermediatepart 70 is bent radially outwards and serves the same purpose as theannular flange 36 according to the embodiment represented in FIG. 2, andthe third part 12 of said lugs extending axially forwards and servingthe same purpose as the cylindrical flange 38 according to theembodiment represented in FIG. 2. At its front end, the wall 32 isconnected to an annular flange 34, in the same way as in the precedingembodiment.

FIG. 6 shows another variant, in which the cage 30 comprises a wall 32,in the shape of a truncated cone at least at its rear part while it maybe cylindrical at its front part, and lugs 74 consisting of partial cutsin the rear part of the wall 32, such lugs 74 extending forwardssubstantially parallel to the axis of the cage from the rear end of thelatter, on a length corresponding to that of the cylindrical flange 38according to the embodiment illustrated in FIG. 2. At its front end, thecage comprises an annular flange 34, which is directed radially inwardsin the same way as in the preceding embodiments.

Another variant of the cage, as shown in FIGS. 7 and 8, correspondsfundamentally to the embodiment as per FIG. 2, and it comprises atruncated-cone shaped wall 32, extending between a front annular flange34 and a rear annular flange 36, including openings 48 and united with acylindrical flange 38, the rear annular flange 36 further comprisingprotruding studs 76, which extend axially rearwards and constitute theabutting means of the cage 30 against the inner shoulder 64 of thehousing 20.

As far as all these embodiments are concerned, the cage 30 is fastenedinside the housing 20 in the above-described manner, in which there isno contact whatsoever either with the inner wall of the housing 20 orthe edges and root of the annular groove 44, thus precluding any removalof metal particles or chips.

It should also be noted that, in the embodiments shown in FIG. 5 through8, the cage 30 does not have to be axially movable inside the housing inorder to keep clear, of the end part of such housing, openingsfacilitating the pressure-fluid flow through the passage 24.

1. A master cylinder piston, more particularly for a motor vehicle,comprising at one end a substantially cylindrical housing (20)accommodating a flap (22) and a return spring (28) arranged between theflap and a cage (30), added to the piston, characterised in that saidcage (30) is crimped inside the housing (20), characterised in that thecrimping process is carried out using retaining means (38, 72, 74),which are formed on the cage and accommodated, under a plasticdeformation effect, in an annular groove (44) provided in said housing.2. The piston according to claim 1, characterised in that the cage (30)is movable inside the housing, on a distance corresponding to the axialplay or its retaining means within the annular groove (44).
 3. Thepiston according to claim 1, characterised in that the retaining meanscomprise a substantially cylindrical flange (38) extending round thecage in the direction of the open end of the housing (20).
 4. The pistonaccording to claim 1, characterised in that the retaining means compriselugs (72, 74), extending substantially parallel to the axis of the cagearound the latter in the direction of the open end of the housing (20).5. The piston according to claim 4, characterised in that said lugs (72,74) are formed either by partial cuts or cutouts made in a substantiallycylindrical or truncated-cone shaped wall (32) of the cage.
 6. Thepiston according to claim 1, characterised in that the cage (30)comprises, on the side of the flap (22), bearing means (36, 76) intendedto rest on an inner shoulder (64) of the housing.
 7. The pistonaccording to claim 1, characterised in that the end of the cage, on theopen end side of the housing (20), comprises an annular flange (34)directed radially inwards and constituting bearing means for the returnspring (28) of the flap.
 8. The piston according to claim 1,characterised in that said cage is manufactured using a stampingprocess.
 9. A jig for the fitting of a flap into a master cylinderpiston, more particularly for a motor vehicle, said piston (10)comprising, at one end, a substantially cylindrical housing (20)accommodating a flap (22) and a return spring (28) arranged between theflap and a cage (30), added to the piston and fastened using retainingmeans received within an annular groove (44) made in the cylindricalwall of the housing (20), characterised in that: in an initial freestate, said cage (30) has an outer diameter which is smaller that theinner diameter of the housing (20); the housing (20) includes means (64)for the axial support of the cage (30) in a position in which itsretaining means (38, 72, 74) are radially in line with said annulargroove (44); and the jig comprises means (52) for the support andapplication of the cage (30) onto the supporting means (64) of thehousing, and means (54) for a radially-outward deformation of saidretaining means of said cage, so as to introduce them into the annulargroove (44) provided in the housing.
 10. The jig according to claim 9,characterised in that the means f or the application of the cage (30)onto the supporting means (64) of the housing comprise a central pushrod (52), fitted inside a tubular member (54), a bevelled end (56) ofwhich constitutes said radial-deformation means.
 11. The jig accordingto claim 10, characterised in that the central push rod (52) is guidedfor an axial sliding motion within said tubular member (54), and biasedby a return spring (58) in a direction which corresponds to the applyingof the cage (30) onto the supporting means (64), formed in the housing.